Semiconductor laser device and optical disc drive

Abstract

A 780 nm band semiconductor laser device has an InGaAsP well layer, phosphorous composition of which is 0.51 smaller than 0.55 to prevent spinodal decomposition in growing InGaAsP. A compressive strain of 0.65% less than 1% and more than 0.25% is introduced into the well layer to reduce threshold current thereof. Thus, the 0.78-μm band semiconductor laser device having the InGaAsP well layer stably operates for a long time even in outputting a high optical power of 100 mW or more. A tensile strain of 1.2% is also introduced into barrier layers within the active region so as to compensate the stress due to the compressive strain of the well layer. As a result, the reliability of the semiconductor laser device is further increased during a high output operation.

1. A semiconductor laser device having an oscillation wavelength of more than 0.76 μm and less than 0.8 μm, the semiconductor laser device comprising:
 a first conductive-type cladding layer; 
 a first guide layer; 
 a strained quantum well active region including a well layer to which a compressive strain is introduced; 
 a second guide layer; and 
 a second conductive-type cladding layer, at least which are sequentially stacked on a GaAs substrate, wherein 
 the well layer is formed of InGaAs l−x P x , and wherein x<0.55, and
   { a (well)− a (GaAs)}/ a (GaAs)×100<0.8% 
 
 where a(well) is defined as a lattice constant of a constituent material of the well layer, and 
 where a(GaAs) is defined as a lattice constant of the GaAs substrates, and the laser device has an oscillation wavelength of more than 0.76 μm and less than 0.8 μm. 
 
     
     
       2. The semiconductor laser device according to  claim 1 , wherein a value of [{a(well)−a(GaAs)}/a(GaAs)]×100 representing a strain amount of the well layer is more than 0.25%. 
     
     
       3. The semiconductor laser device according to  claim 1 , wherein a value of x that represents a P composition in Group V elements of the well layer is smaller than 0.50. 
     
     
       4. The semiconductor laser device according to  claim 1 , wherein the well layer has a strain amount of less than 0.5%. 
     
     
       5. The semiconductor laser device according to  claim 1 , wherein the strained quantum well active region includes a barrier layer into which a tensile strain is introduced. 
     
     
       6. The semiconductor laser device according to  claim 1 , wherein the well layer has a layer thickness larger than 8 nm. 
     
     
       7. An optical disc unit wherein the semiconductor laser device according to  claim 1  is used as a light-emitting device.